The sea grass Posidonia oceanica, a clonal species, is the dominant habitat forming, foundation species in coastal areas of the Mediterranean Sea. This species also provides additional ecosystem services through its role in stabilizing shorelines and immense primary productivity. Over the last century and particularly over the last 50 years, P. oceanica meadows have been contracting, in large part due to anthropogenic factors, and there has been considerable effort directed at restoration of degraded meadows. These efforts have almost always involved the transplantation of rhizomes, under the assumption that expansion and local replenishment of meadows would occur via vegetative growth. These efforts have met with little success. The PIs challenge the prevailing assumption that sexual reproduction for this clonal species is largely unimportant to population demography and rescue. They will take advantage of a recent and on-going mass flowering of P. oceanica at several sites in the northern Mediterranean. Preliminary data from one of the sites show spatial patterns of flowering within the sea grass communities. If these patterns are related to clones, identified through genetic analysis, that knowledge could be of great help in conserving and restoring local populations of this species. It would also shed light on a fundamental question about the relative functioning of sexual and asexual reproductive modes in a long-lived species. Flowering events such as the ones now taking place are both rare and unpredictable, making this an unusually good opportunity for this project.
Broader Impacts: This work began as a student project under the direction of the PIs, and the two female undergraduate students involved in the initial project will play a primary role in the research described in this proposal, under appropriate supervision and with new training in molecular techniques. Results will provide new insights that could be very useful in conservation and restoration biology.
The general goal of this project was to describe the fine scale spatial genetic structure (SGS)of the clonal seagrass Posidonia oceanica within a meadow in the Bay of Calvi, Corsica. Our specific goals were to use the fine scale SGS to: 1) Assess the contribution of local sexual reproduction to the population genetic structure of the meadow. 2) Determine the characteristic spatial scale (size) of clones 3) Determine if either 1 or 2 varied as a function of depth of the meadow The last question was based on the tradeoff between reproduction and clonal growth and the ideas that (a) light required for growth and reproduction was limiting at depth and (b) disturbance decreased with depth. We found that local sexual reproduction leading to local recruitment was much more likely in shallow areas compared to deeper ones (figure 1) and that clone size was smaller in shallow areas compared to deeper ones (figure 2). Neither result had previously been described although both fit in the context of what is known about the ecology of clonal seagrass and the life-history of P.oceanica in particular. Our second result in particular suggests that the role of sexual reproduction in shaping the spatial genetic structure of a meadow may have been underestimated. Our results have considerable implications for meadow restoration, which is widely advocated as a means to counter widespread loss in the Mediterranean. This work was initiated based on a project done by two undergraduates in the Marine Biology Field Quarter class at UC Santa Cruz (Emily Tucker and Hannah Perlkin). As a result of the awarding of the grant, both women were employed to do the NSF sponsored research (and have continued working at UC Santa Cruz). This included: development of spatial sampling design, internships in both France and Portugal in labs expert in molecular genetics of P.oceanica, intensive field work in Calvi and subsequent analysis and manuscript preparation at UC Santa Cruz.
